Several trends presently exist with regards to wireless communication devices. For example, in comparison to previous generations of wireless devices, modern wireless devices are more compact, more affordable, and have longer battery lifetimes. While consumers may largely take these trends for granted, these trends are the result of significant engineering efforts.
To communicate with other devices, many wireless devices include receivers. These receivers are typically included in chip sets that enable wireless communication via one of several communication standards, such as Bluetooth, Digital Enhanced Cordless Telecommunication (DECT), and numerous others. Because these chip sets are used commonly in cell phones, music players, personal digital assistants (PDAs), etc., it is desirable for the chip sets to be relatively compact and efficient, thereby providing lower cost, higher performance products in a smaller footprint.
In recent years, one way in which designers have tried to deliver compact and efficient chipsets is by including zero intermediate frequency (IF) receivers. A zero IF receiver enables direct conversion of analog radio frequency (FREQ) signals to a digital baseband. This typically reduces the component count, and may correspondingly limit the footprint and cost of the chipset. By reducing the number of components, zero IF receivers also simplify the supply chain and improve manufacturing yield.
While zero-IF receivers offer a more compact chipset, technical barriers often limit the extent to which such receivers can be used in modern communication systems. For example, because a local oscillator signal (LO) in these receivers is the same as the RF frequency, the LO signal may leak from the receiver to the antenna, which can cause interference with other receivers on the same frequency-band. Also, DC offset, which comes from the self-mixing of LO leakage, may seriously deteriorate the SNR (Signal Noise Ratio).
One type of receiver that limits both of these shortcomings (i.e., LO leakage and DC offset) is a low-IF receiver. In low-IF receivers, the received RF frequency is down-converted to a low, but non-zero IF, before being down-converted to the baseband. Thus, the down-conversion from the received RF frequency to the baseband will have one or more IFs, where each IF corresponds to a separate stage in the receiver. Due to the fact that these separate stages are relatively area intensive, conventional low-IF receivers have a relatively large footprint.
In order to continue to meet and exceed consumers' growing expectations with regards to compactness, affordability, and battery life; improved low IF receivers are needed. Ideally, these improved low-IF receivers will provide relatively high-performance in a relatively small footprint.